This invention relates to improvements in or relating to dry powder inhalers, in particular dry powder inhalers of the type that comprise first and second medicament reservoirs that hold bulk quantities of two different medicaments, and which have associated therewith respective rotatable first and second metering members by which doses of the two medicaments are simultaneously dispensed for simultaneous inhalation by a patient.
Dry powder inhalers of the type with which the invention is concerned are disclosed in International patent applications WO-A-01/39823, WO-A-2005/102429 and WO-A-2005/102430. In the inhalers disclosed in those documents, each medicament reservoir is associated with a rotatable metering member, typically of frustoconical form, the surface of which is provided with depressions that constitute cups for the volumetric metering of a dose of medicament. The metering member is pressed into close engagement with an opening in the reservoir by a compression spring and a lower part of the reservoir assembly constitutes a support for the metering member, within which the metering member rotates. The two metering members rotate about a common axis, the compression spring being mounted between them and urging them outwardly into engagement with the respective supports. An actuator, eg a manually operated push button, causes the metering members to rotate in unison and to transfer doses of the two medicaments from the reservoirs to a position from which the doses can be inhaled by the patient.
In a device of the type described above, it is important that the seal between the metering members and their respective support structures should be as tight as possible, to minimise the possibility of ingress of moisture into the medicament reservoirs, since moisture may cause degradation of the medicaments, and/or faulty operation of the dosing mechanism, and/or agglomeration of the medicament powders, all of which (as is well known) have adverse therapeutic consequences for the patient. It is also important that the metering members should be coupled together in such a way that they operate in unison, so that medicaments that are intended to be administered together are indeed so administered. Despite these requirements, it is also important that the device should be easily and reliably manufacturable.
There have now been devised improvements to dry powder inhalers of the type generally described above that address the above mentioned requirements and/or other disadvantages of the prior art.